A C-Band FMCW SAR Transmitter Based on Synthetic Bandwidth Technique

Abstract

A $C$ -band frequency-modulated continuous wave (FMCW) transmitter based on synthetic bandwidth technique for synthetic aperture radar (SAR) imaging is presented. A 500-MHz narrowband chirp signal is up-converted to two adjacent carriers to obtain 1-GHz chirp at the $C$ -band. The adjacent carriers are obtained through fast switching subharmonic injection locking oscillator (SHILO) technique with 14-ns settling time. For narrowband chirp, a wideband fractional- $N$ phase locked loop (PLL) is used, covering 1.8–2.3 GHz and achieving low in-band phase noise of −115 to 120 dBc/Hz. The proposed technique achieves reconfigurable chirp period ranging from 0.3 to 6.3 ms. It can also be easily extended for wider chirp bandwidth by simply increasing the number of SHILO carriers. The chip consumes 84 mW, while occupying a total active area of 2.24 mm2.